plugins: correctly output build version, cosmetic cleanups

Now that libcni has the ability to print a version message, plumb it
through correctly.

While we're at it,
- fix import paths
- run gofmt
- add some more comments to sample
- add container runtime swappability for release

plugins/ipam/dhcp/main.go

@@ -27,6 +27,7 @@ import (
 	"github.com/containernetworking/cni/pkg/types"
 	"github.com/containernetworking/cni/pkg/types/current"
 	"github.com/containernetworking/cni/pkg/version"
+	bv "github.com/containernetworking/plugins/pkg/utils/buildversion"
 )
 
 const defaultSocketPath = "/run/cni/dhcp.sock"
@@ -51,8 +52,7 @@ func main() {
 			os.Exit(1)
 		}
 	} else {
-		// TODO: implement plugin version
-		skel.PluginMain(cmdAdd, cmdCheck, cmdDel, version.All, "TODO")
+		skel.PluginMain(cmdAdd, cmdCheck, cmdDel, version.All, bv.BuildString("dhcp"))
 	}
 }